Defrosting without
cracking the screen

Glass expands when it warms and contracts when it cools. Do that unevenly and fast, across a pane that already has a flaw in it, and the flaw is where it gives.

The three fastest ways to lose a windscreen

• Hot air aimed straight at frozen glass on full blast. The inside warms, the outside does not, and the stress goes to the weakest point.
• A kettle, a jug, or any warm water. This is the classic, and it cracks screens that had no visible damage at all.
• Scraping hard directly over a chip. The flex is enough to run the legs of a star break.

What to do instead

1. Start the engine and set the heater to a low or medium setting, aimed at the screen, and leave it. Turn on the air conditioning if you have it: it dries the air and clears the inside faster.

Then get out and scrape the outside with a proper plastic scraper while the cabin warms. Work away from any chip you know about rather than over it. De-icer spray on the stubborn edges is fine and will not harm the glass.

The whole thing takes five minutes rather than one. It is a lot cheaper than the alternative.

If you already have a chip

Cover it with a piece of clear tape before the cold sets in. That keeps water and grit out of the break, which matters twice over: moisture in a break freezes and expands, and dirt in a break stops resin bonding properly later.

Then get it repaired before the first hard frost rather than after. A repair is forty minutes and usually nothing to pay. A replacement is most of a morning, plus recalibration on most modern cars.

Overnight, if you can

A windscreen cover is the simplest answer of all: no ice to remove means no temperature shock. A folded sheet under the wipers works nearly as well.

Parking nose-away from the prevailing wind, or under any kind of cover, also helps more than people expect.